Fuel assemblies used inter alia in PWRs comprise a bundle of fuel elements (each formed by a stack of pellets in a fluid tight sheath) held in place in a structure. This latter comprises grids spaced apart along the assembly, each formed by plates disposed along two orthogonal directions, to define cells. Most cells accomodate fuel elements. Each of such cells is provided with means engaging the fuel element which passes through the cell for supporting it.
The supporting means may be formed by cut-out parts of the plates, forming lugs bearing against the rods. But it is of advantage to use springs fastened to the plates and made of a material different from the plates. A grid of the latter type is described, for example, in French Pat. No. 2,474,229 to which reference may be made.
The springs have in general a hair-pin shape with two legs. There is frequently a need for several types of spring in the same grid since the grid has lateral walls and some cells accomodate elements other than fuel elements, e.g., by guide tubes. One of the types will frequently comprise two identical legs whereas another type will have legs of different shapes. The springs are first inserted, then secured to the plates by welding the two legs together at predetermined points, between which are located windows formed in the grid plates. The positioning of each spring is tricky: it is necessary to locate each spring accurately so as not to weld it on the plate and to avoid contamination. Up to now, the springs have been located and welded manually, which is time consuming and tedious, and further likely to give rise to errors when springs of different types must be placed at well-defined locations on the plate. It may be thought that one of the reasons why this procedure has not been automated resides in the risks of catching the legs of the springs on the numerous unevenesses of the plate during insertion of a spring whose legs are spaced apart by a distance which may not be exactly defined because of their resilience.